Thermostatic switch

ABSTRACT

A thermostatic switch is disclosed comprising a dielectric housing having a first switch contact mounted within the housing. A thermoresponsive element having a central aperture is provided with a second switch contact mounted to the thermoresponsive element to make and break with the first switch contact upon actuation of the thermoresponsive element. A screw is screwed into the housing with a screw head disposed above an interior surface of the housing and a screw shank passing through the thermoresponsive element central aperture between the screw head and the housing interior surface. The central portion of the thermoresponsive element about the aperture is free to move along the screw shank between the screw head and housing interior surface. With this arrangement the screw provides means for adjusting the disposition of the thermoresponsive element while the screw head and housing interior surface limit movement of the central portion of the thermoresponsive element.

United States Patent .1

Woods Aug. 14, 1973 THERMOSTATIC SWITCH Primary Examiner-Harold Broome[75] Inventor: Lee 0. Woods, Morrison, Ill. Attorney-John Stoudt et [73]Assignee: General Electric Company, Fort Wayne, Ind. ABSTRACT [22]Filed: Sept. 20, 1972 A thermostatic switch is disclosed comprising adielectric housing having a first switch contact mounted [21] Appl'290570 within the housing. A thermoresponsive element having a centralaperture is provided with a second switch [52] U.S. Cl 337/347, 337/368,337/94 Contact mounted to h herm responsive element to [51 Int. Cl. H01h37/20 make and break h h first switch contact upon actu- [58] Field ofSearch 337/347, 368, 343, ation of the rm r pon i element. A screw is337/363, 367, 89, 86, 94, 57 screwed into the housing with a screw headdisposed above an interior surface of the housing and a screw [56]References Cit d shank passing through the thermoresponsive elementUNITED STATES PATENTS central aperture between the screw head and thehousing interior surface. The central portion of the thermogt g firesponsive element about the aperture is free to move 2 434 984 1/1948Boleskfiiliffi II: 337/367 alng the Screw shank between the screw headand 3,1950 Bolesky 337/89 housing interior surface. With thisarrangement the 2,543,040 2/1951 Mertler... 337 screw provides means foradjusting the disposition of 2,866,039 12/1958 Epstein 337/89 thethermoresponsive element while the screw head 2,967,920 1/1961 Harper,Jr. et al. 337/86 and housing interior surface limit movement of thecen- 3,0|3,l38 [2/1961 MOkSLI {It a]. 337/94 tra] portion of thethermoresponsive element 3,393,389 7/1968 Mawney et a1. 337/57 10Claims, 4 Drawing Figures 1 l 53 5g 7 i I .5? 40 T 40 J 42 e 42 1 -.1 Hi A I l I I0 I I /4 24 54 Patented Aug. 14, 1973 3,753,195

2 Sheets-Sheet 1 i, 86 3 EB Patented Aug. 14, 1973 3,753,195

2 Sheets-Sheet 2 THERMOSTATIC SWITCH,

BACKGROUND OFTI'IE INVENTION arcuate bimetallic sheets or discs.Usually, the disc is mounted within the switchzhousingby means of anad'- justable screw or postpassing through an aperture in: the disccenter. Upon heating the disc snaps bringing.

switchcontacts mounted onthe disc periphery into or our of engagementwith: matingaswitchcontacts fixedly mounted. within the switch housingadjacent the disc.

Reciprocal movement occurs upon cooling. Disc heating may. be effectedeither by; changes in ambient-temperature or by means-of'anv electricheating elementmounted within the: switch housing adjacent the' disc.

Inorder for. the arcuate' bimetallic disc to snap and thereby reverseits curvature;.i.e. t have its concave surfacebecomeconverrand-itsconvexsurface become concave, both its central andperipheral: portions must" have some freedom of movement. This movementhowever mustube limited in order. for reversesnapactionto return-the:disc to" its. initialpositionfrom which it may subsequentlybei-recycledl And=,.of.course;.the discmust be properly mounted withinthe switchhousing itself.

Heretofore, the just discussed: requirements have been metmostfrequently. by means of screwsor bolts which,.for thepurpose of'thisapplication and concluding claims, are considered equivalents. The screwis passed loosely througha central aperture in the bimetallicdisc withthe threaded shank portionscrewed'into the housing orinto anut. Thescrewhead'itself or a terminalfastener'has served to limitdisc' movementinone direction. Movement in the opposite" direction away fromthescrew-head has been limited by-flanges formed integrally on the screwshank or secured thereto. In other cases such opposite'disc movementhasbeenlimited by compression sprin'gs disposed about the shank in contactwith ahousingsurface; In still other cases eyelets and arborforming'collars have been secured to such shanks, or, inthe case ofnonadjustable' discs, to posts formed integrally with the housing. Eachof these implements'haveincluded components which, in addition to thedisc. itself, have had: to be secured-to the screw and carefullyadjusted'in calibratingvthe switch. As these thermostaticv switches areoften quite small and manufactured in large quantities, the. necessityfor carefully securing such limits or stops has proven costly.

In thermostaticv switches of the type just described the peripheralportionsi of the thermoresponsive'element mustalso havelimited freedomof movement'in order to actuate the switch contacts associatedtherewith. Thus, theperipheral portion ofthe element is usually disposedwithinacavity or void within theswitch housing. When an internal heatingelement is employed such heater is also disposed withinthis-cavityadjacent the thermoresponsive element. To the walls encompassing, andfrequently definingthe cavity itself, are

mounted the switch terminals which extendto the exte-- rior of theswitch housing. Frequently, one or more switch contacts aremounteddirectly to a portion of these terminals which protrude into thecavity. The

housing is typically formed of a molded phenolic resin. The metallicterminals are securedto' the housing by means of a thermosettingadhesive=such= as an epoxy resin. During-manufacture it is difficultto'control fully the" flow of the thermosetting adhesive; Thus,'it oftenhappens that a portion of the adhesive fiows down into the cavity andonto a portion of the heating element. This, of course, is not desiredinsomuch as the resultant adhesive bridge fromthe housing to the heatercreates a thermally conductive path for heat to flow to the housingrather than be radiated and convected to the thermoresponsive disc. Thistends to place the thermostatic switch out'ofi operational adjustment.In addition, adhesiveupon the heater'tends to be vaporized during heateroperation, which vaporized adhesive may condense upon the cooler switchcontacts and otherwise contaminate the switch interior.

Accordingly, it is a general'object of the present invention to providean improved thermostatic switch of the type employing a snap-actingthermoresponsiveelement.

More specifically, it is an object of the invention to provide'athermostatic switch having improved means for adjustably mounting andlimiting movement of a snap-acting thermoresponsive element.

Another'object of the invention is to provide a thermostaticswitchhaving a'snap-acting thermoresponsive element with improvedmeans'forpositioninga heating element within the switch housing adjacent thesnapacting thermoresponsive element.

SUMMARY OF THE INVENTION In one form of the present invention athermostatic switch is provided comprising adiel'ectric housing having afirst switch contact mounted within the housing. A thermoresponsiveelement having a central'aperture is provided with a second switchcontact mounted to the thermoresponsive element to make andbreakwith thefirst switch contact upon actuation of the thermoresponsive element. Ascrew is screwed into the housing I BRIEF DESCRIPTION OF THE DRAWINGFIG. 1 is a top plan view of a thermostatic switch em-' bodyingprinciples of the present invention in one form with most of the housingcover removed to reveal internal components of the switch. I

FIG. 2 is a cross-sectional view of the switch show in FIG. 1 takenalong plane 2-2 with selected switch terminals, contacts, and anadjustable screw shown in elevation. I

- FIG. 3 is a topplan view of the switch housingcover shown in FIG. 2.

FIG. 4 is a top plan view of the switch housing base shownin FIGS. 1 and2.

DETAILED DESCRIPTION OF THE DRAWING Referring now in more detail to thedrawing, there is shown a thermostatic switch comprising a dielectrichousing having a molded phenolic base member and a molded phenolic covermember 12. The two housing members are secured together along mating,planar member surfaces by four screws 14 extending through aligned holes16 in the two housing members, and by four nuts 18.,Alternatively,rivits or eyelets may be substituted for these screws and nuts. Theinterior of base 10 may, by reference to FIG. 4, be seen to be so moldedas to have three walls 20 peripherally disposed about a cavity floor 22.Three steps 24 rise above floor 22 with the top surface of the stepsextending between walls 20 to the base exterior. Each step has a recess26 in the top surface as well as a trough 28 extending downwardly fromthe recess towards the cavity floor.

From the central portion of the cavity floors extends a generally conicprojection 30 having a center bore 32 into which a screw may be screwedand thereby form threads within the bore. The conic projection istruncated to have an annular, planar apex surface 34. Near thisprojection apex surface bore 32 flares as shown by conic surface 36. Asseen by reference to FIG. 3, cover 12 is molded with walls 38 formed tomatewith the walls of base 10. When so mated upon switch assembly wallextensions 39 project partially down over the extensions of steps 24between base walls 20 thereby forming three slots which pass through themated walls to the switch exterior.

Referring now to FIGS. 1 and 2 the thermostatic switch is seen to havethree generally planar terminals 40 extending from the exterior of theswitch housing through the just described slots and onto the top ofsteps 24 between shoulders 25. To the exposed tops of two of theseterminals are secured two stationary or fixed switch contacts 42. Aheater wire 44 is secured to the third terminal and to one of thecontact supporting terminals. The heater wire partially encirclesprojection 30 in spaced relation with both it and floor 22 of the cavityin which it is disposed. Terminal tabs 46 extend downwardly intorecesses 26 within steps 24. A thermosetting adhesive, such as atranslucent epoxy resin, is poured into recesses 26 as indicated at 48.Once set the adhesive firmly secures terminals 40 atop steps 24 and thusto the housing base. During manufacture excess adhesive flows downthrough troughs 28 to cavity floor 22. The quantity of adhesive inexcess to the volumetric capacity of recesses 26 is ordinarily slightand certainly insufficient to cover floor 22 and thereby build upwardlytowards heater wire 44. Being below the top surface of the terminalsthere is also little danger in any of the adhesive flowing onto contacts42.

With continued reference to FIGS. 1 and 2, a thermoresponsive element inthe form of a generally disc shaped sheet of bimetal 50 is seen to bemounted within the switch housing by means of a screw having a screwhead 52 and a screw shank 54. One of two unitary tail portions 51 of thedisc are positioned between two posts 53 which prevent the disc fromrotating. An unthreaded portion of the screw shank passes looselythrough a central aperture 56 in the bimetallic disc. The centralaperture is in the shape of a four leaf clover which serves to providethe disc with good snap action characteristics during actuation. Athreaded portion of the screw shank is screwed into the walls of bore 32within projection 30 until screw head 52 engages the bi-metallic discwith mobile switch contacts 58 secured beneath peripheral portions ofthe disc in engagement with fixed contacts 42. The screw may then bescrewed further down into bore 32 for switch operational adjustment. Asthis action progresses screw head 52 forces the central portion of disctowards annular surface 34 atop projection 30 whereupon a smallerincrease in the temperature of the disc will cause the disc to snap tothe position shown in phantom lines 50'. Such snap action in turn causesswitch contacts 42 and 58 to break. Subsequent cooling of the discforces the disc to snap back to its initial position 50 thereby causingthe fixed and mobile contacts to remake.

From the above description it should be noted that screw head 52 limitsmovement of the central portion of the bimetallic disc upwardly, asviewed in FIG. 2, while annular surface 34 atop conic projection 30limits downward movement of this portion of the disc. Thus, screw head52 and annular surface 34 function as stops. Simultaneously, screw head52 serves as disc mounting and adjustment means, and annular surface 34as a part of the female screw receiving and switch housing structure.This unique combination of elements renders simplicityv and economy tothe switch.

It should be understood that the just described embodiment merelyillustrates principles of the invention. Obviously, many modificationsmay be made thereto without departure from the spirit and scope thereofas set forth in the following claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A thermostatic switch comprising a dielectric housing; at least onefixed contact mounted within said housing; a conductive snap-actingthermoresponsive element having a centrally located aperture; at leastone mobile switch contact mounted to said conductive snap-actingthermoresponsive element to make and break with said fixed switchcontact; and a screw secured to said housing and having an exposed screwshank portion extending from an interior surface of said housing throughsaid thermoresponsive aperture to a screw flange portion extending overa portion of said thermoresponsive element adjacent saidthermoresponsive element aperture, said exposed screw shank portionbeing dimensioned to permit the central portion of said thermoresponsiveelement to move there-, along between said housing interior surface andsaid screw flange portion; whereby the screw provides means foradjusting the disposition of the conductive snap-acting thermoresponsiveelement, and the interior housing surface and screw flange portion limitmovement of the central portion of the conductive snapactingthermoresponsive element along the exposed shank portion of the screw.

2. A thermostatic switch in accordance with claim 1 wherein said screwflange portion comprises the, head of said screw.

3. A thermostatic switch in accordance with claim 1 wherein saidinterior surface of said housing is annular.

4. A thermostatic switch in accordance with claim 1 wherein saiddielectric housing comprisesa base having an interior floor and acentrally located projection extending from said floor; and wherein saidinterior surface of said housing is the apex of said projection.

5. A thermostatic switch in accordance with claim 4 wherein said basecomprises a plurality of steps extendin g from said floor in spacedrelation with said centrally located projection; and a plurality ofwalls extending between said steps to form a cavity within said basebounded on the outside by said walls and steps and on the inside by saidcentrally located projection.

6. A thermostatic switch in accordance with claim 5 comprising aplurality of terminals mounted atop said plurality of steps, and aheater wire disposed within said cavity adjacent said conductivesnap-acting thermoresponsive element and electrically connected to twoof said terminals.

7. A thermostatic switch comprising: a dielectric housing; a firstswitch contact mounted within said housing; a thermoresponsive elementhaving a central aperture; a second switch contact mounted to saidthermoresponsive element to make and break with said first switchcontact upon actuation of said thermoresponsive element; a screw screwedinto said housing and having a screw head disposed above an interiorsurface of said housing and a shank passing through saidthermoresponsive element central aperture between said screw head andsaid housing interior surface with the central portion of saidthermoresponsive element about said aperture being free to move alongsaid shank between said screw head and said housing interior surface;whereby said screw provides means for adjusting the disposition of saidthermoresponsive element and wherein said screw head and housinginterior surface limit movement of said thermoresponsive element.

8. A thermostatic switch in accordance with claim 7 wherein saiddielectric housing includes a base having a centrally located projectioninto which said screw is screwed, and wherein the apex of saidprojection forms said housing interior surface.

9. A thermostatic switch in accordance with claim 8 wherein said housinginterior surface is the annular apex of a truncated conic projectioninto which said screw is screwed.

10. A thermostatic switch in accordance with claim 9 wherein saidhousing base has a plurality of peripheral walls disposed about saidcentrally located projection at least partially defining a cavity, andwherein said thermostatic switch further comprises means for heatingsaid thermoresponsive element mounted within said cavity in spacedrelation with said walls and said projection. I

* i i I k

1. A thermostatic switch comprising a dielectric housing; at least onefixed contact mounted within said housing; a conductive snap-actingthermoresponsive element having a centrally located aperture; at leastone mobile switch contact mounted to said conductive snap-actingthermoresponsive element to make and break with said fixed switchcontact; and a screw secured to said housing and having an exposed screwshank portion extending from an interior surface of said housing throughsaid thermoresponsive aperture to a screw flange portion extending overa portion of said thermoresponsive element adjacent saidthermoresponsive element aperture, said exposed screw shank portionbeing dimensioned to permit the central portion of said thermoresponsiveelement to move therealong between said housing interior surface andsaid screw flange portion; whereby the screw provides means foradjusting the disposition of the conductive snap-acting thermoresponsiveelement, and the interior housing surface and screw flange portion limitmovement of the central portion of the conductive snap-actingthermoresponsive element along the exposed shank portion of the screw.2. A thermostatic switch in accordance with claim 1 wherein said screwflange portion comprises the head of said screw.
 3. A thermostaticswitch in accordance with claim 1 wherein said interior surface of saidhousing is annular.
 4. A thermostatic switch in accordance with claim 1wherein said dielectric housing comprises a base having an interiorfloor and a centrally located projection extending from said floor; andwherein said interior surface of said housing is the apex of saidprojection.
 5. A thermostatic switch in accordance with claim 4 whereinsaid base comprises a plurality of steps extending from said floor inspaced relation with said centrally located projection; and a pluralityof walls extending between said steps to form a cavity within said basebounded on the outside by said walls and steps and on the inside by saidcentrally located projection.
 6. A thermostatic switch in accordancewith claim 5 comprising a plurality of terminals mounted atop saidplurality of steps, and a heater wire disposed within said cavityadjacent said conductive snap-acting thermoresponsive element andelectrically connected to two of said terminals.
 7. A thermostaticswitch comprising: a dielectric housing; a first switch contact mountedwithin said housing; a thermoresponsive element having a centralaperture; a second switch contact mounted to said thermoresponsiveeleMent to make and break with said first switch contact upon actuationof said thermoresponsive element; a screw screwed into said housing andhaving a screw head disposed above an interior surface of said housingand a shank passing through said thermoresponsive element centralaperture between said screw head and said housing interior surface withthe central portion of said thermoresponsive element about said aperturebeing free to move along said shank between said screw head and saidhousing interior surface; whereby said screw provides means foradjusting the disposition of said thermoresponsive element and whereinsaid screw head and housing interior surface limit movement of saidthermoresponsive element.
 8. A thermostatic switch in accordance withclaim 7 wherein said dielectric housing includes a base having acentrally located projection into which said screw is screwed, andwherein the apex of said projection forms said housing interior surface.9. A thermostatic switch in accordance with claim 8 wherein said housinginterior surface is the annular apex of a truncated conic projectioninto which said screw is screwed.
 10. A thermostatic switch inaccordance with claim 9 wherein said housing base has a plurality ofperipheral walls disposed about said centrally located projection atleast partially defining a cavity, and wherein said thermostatic switchfurther comprises means for heating said thermoresponsive elementmounted within said cavity in spaced relation with said walls and saidprojection.